Installation for the separation of fluids

ABSTRACT

An installation arranged on the sea bed for the separation of fluids, comprising at least one separator ( 1 ) that is connected to one or more wells, each via an associated well head ( 2 ) or similar, and a pipeline ( 17 ). The components separated, oil, gas, water or combinations of these substances, are fed fully or partially from the installation to a platform, vessel, etc. on the surface or via collecting pipelines onto shore, or are reinjected into the formation beneath the sea bed. Each separator ( 1 ) consists of a long pipe (pipe separator) that may form a major or minor part of the transport pipeline ( 18 ) from the well and has a diameter that is mainly equal to or slightly larger than the diameter of the transport pipeline ( 18 ).

The present invention concerns an installation arranged on the sea bedfor the separation of fluids.

Fluids in this context means oil, gas and water or mixtures of thesesubstances, possibly containing particles of sand, that are produced inconnection with the extraction of oil/gas from wells in geologicalformations beneath the sea bed.

PCT/NO98/00085 concerns the separation of fluids in pipe separators inhorizontal sections of wells.

The main reason why it is possible to achieve quantitative oil and waterseparation in a pipe separator installed in a horizontal well is relatedto the good separation properties of the well fluid. The main reason forthe good separation properties in the well is that the interface betweenthe oil and water is relatively free of surfactants that can stabilisethe interface and thus impede drop growth and the formation of a freeaqueous phase in connection with coalescence. This is what makes itpossible to use such separation solutions in the well, where controlleduse of a de-emulsifier is very complicated or virtually impossible.

In many cases, it may be desirable to carry out the separation on thesea bed instead of in the wells. On the sea bed, chemicaldestabilisation of the crude oil using a de-emulsifier is a much simplerand absolutely realistic solution. Chemical destabilisation of the fluidcan improve the separation properties of the fluid so that they arealmost as good as down-hole conditions. This makes it possible to usepipe separator technology on the sea bed in connection with sea bedprocessing plants. With a sea bed installation, there is also greaterfreedom with regard to the choice of separator diameter than with adown-hole installation.

Conventional gravitation separators are characterised by large tankdiameters. This limits the application of the technology to relativelyshallow waters. Long, thin separators with high UD ratios are favourablefor use at large sea depths.

Under typical sea bed conditions, the separation properties of theoil/water fluid will always be poorer than under down-hole conditions.This difference can be compensated for by placing the separator upstreamof the choke when using a de-emulsifier or ultrasound. This makes itpossible to use pipe separators on the sea bed. In practice, the pipeseparator can be a transport pipeline designed with a slightly largerdiameter than necessary or as an extended section of the transportpipeline. The pipe separator is an effective solution to the designproblem caused by high external liquid pressure at large sea depths. Thetechnology can be combined with CEC (Compact Electrostatic Coalescer)concepts based on pipe coalescers, which allows it to be used at largersea depths. For fluids that are more difficult to separate, a CEC isnecessary to achieve the product specifications of the oil phase and toeliminate downstream hydrate precipitation problems in this flow.

The advantages of using a pipe separator in a sea bed processing plantare, among other things, that it allows:

-   -   bulk gas/oil/water separation    -   removal of water from crude oil to product specifications    -   purification of production water to a quality that allows        reinjection    -   purification of production water to a quality that allows it to        be discharged    -   chemical-free hydrate control in connection with the transport        of crude oil and gas.

In the main, the pipe separator produces bulk oil/water separation. Forlighter, simpler crude oil systems, the separator will be able toseparate the fluid down to product specifications. In this case, nofurther separation unit is required in the process. The pipe separatoris designed as follows. The last part of the transport pipeline from thewell head to the processing template is designed as a long, thin pipeseparator. On account of its small pipe diameter (in the order of 0.5m), the separator can be operated at high external pressure and lowinternal pressure. The separator is therefore particularly well suitedfor large sea depths. It is important for the water quality from theseparator to be as good as possible in order to avoid, as far aspossible, any further purification before injection/discharge. Theseparator can therefore be fitted with a mechanical ultrasound-basedemulsion destabilisation system instead of using a chemicalde-emulsifier. This solution will be able to produce a water qualitythat is suitable for reinjection (<<1000 ppm) and possibly for dischargeinto the sea (<40 ppm). A particularly favourable position for the pipeseparator will be at the well head before any pressure relief.

The separator is designed as a three-phase separator with configurationoptions that allow for separate removal of gas, oil and water or,alternatively, gas/oil as a common flow and water as a separate flow. Inaddition, it must also be possible to design the separator as atwo-phase oil/water separator for use downstream from a CEC (CompactElectrostatic Coalescer).

The separator can be fitted with an ultrasound-based destabilisationsystem for the emulsion layer at the oil/water interface (as analternative to the use of chemicals to break up emulsions). Theseparator is also fitted with a double set of level profile meters(alternatives: gamma, capacitance and ultrasound). The end of the pipeseparator is connected to the template either directly or via flexiblehoses.

The present invention will be described in further detail in thefollowing by means of examples and figures, where:

FIG. 1 shows an installation on the sea bed with a pipe separator forgas/liquid separation.

FIG. 2 shows a first alternative embodiment of an installation with apipe separator for gas/oil/water separation.

FIG. 3 shows a second alternative embodiment of an installation with twopipe separators in series, the first for gas/liquid separation and thesecond for oil/water separation.

FIG. 4 shows a third alternative embodiment of an installation with apipe separator for gas/oil/water separation followed by a compactelectrostatic coalescer and subsequently a pipe separator for oil/waterseparation.

FIG. 5 shows a fourth alternative installation with a pipe separator forgas/oil/water separation followed by a compact electrostatic coalescerand subsequently a pipe separator for oil/water separation. In addition,there is a gas dehydration unit consisting of a pipe contactor and agas/liquid separator in connection with the first pipe separator.

FIG. 6 shows a fifth embodiment which is based on the solution shown inFIG. 4, but which is adapted for situations in which two or more wellsproduce different quantities of oil/water/gas.

FIG. 1 shows an installation arranged on the sea bed with a separator inthe form of a pipe (pipe separator) 1 for gas/liquid separation that isconnected to a well head 2. This is a simple solution designed for usefor oil/gas wells in which small quantities of water are produced. Theseparated gas is removed in a pipe 3 and fed up to a platform, aproduction ship, etc. on the surface of the sea or a collecting pipelinethat feeds the gas onto shore. The liquid is removed in a pipe 4, and apump 5 pumps it up to the surface or onto shore as for the gas.

FIG. 2 shows a similar installation to that in FIG. 1. However, inaddition to gas and oil, the separator here also separates out waterthat is fed via a pipe 6 to a pump 7 and back to the reservoir.

FIG. 3 shows a sea bed installation designed for conditions with a lotof gas in relation to liquid. The solution is like that in FIG. 1 butthe liquid (oil and water) that is separated out in a first separator 1is fed to a second separator 8 where the oil is fed to the surface viathe pipe 4 and the pump 5, while the water is reinjected by means of thepump 7 via the pipe 6.

FIG. 4 shows a sea bed processing plant designed for heavier oils andrepresents a further development of the installation shown in FIG. 3.The pipe separator 1, which, in this case, is designed for gas/oil/waterseparation, is connected to the well head 2. The gas is removed in thepipe 3 and fed to the surface. The oil and water proceed to a compactelectrostatic coalescer (CEC) 9 that increases the drop size of thewater. The oil and water are then separated in a second pipe separator 8for oil/water separation. The oil is removed in the pipe 4 and pumped tothe surface by the oil pump 5, while the water is reinjected via thepipe 6 and the reinjection pump 7.

FIG. 5 shows a sea bed installation that, in addition to that which isshown in FIG. 4, has a gas dehydration unit. The gas that is separatedout in the first separator 1 is fed first to a gas dehydration reactor11. Here, glycol is added that “reacts with” the water in the gas. Thegas and the liquid (water dissolved in glycol) are then fed to a thirdseparator 12, which, in turn, separates out the gas, which is fed to thesurface via a pipe 14, while the liquid is fed to a pump 16 and on tothe surface.

FIG. 6 shows an example based on the solution shown in FIG. 4, but whichis adapted for a situation in which different quantities of oil, gas andwater are produced in different ratios from two or more wells. From well2, oil/gas/water are separated in a first separator 1 and oil/water in asecond separator 12 with an intermediate coalescer 9, as explainedpreviously.

Down-hole separation takes place in a second well 20. Water separatedout from the first separator 2, the second separator 12 and thedown-hole separator 18 is fed via respective pipes 21, 22, 23 to abuffer tank 18 for reinjection water. The water in the tank 18 isreinjected into the reservoir by means of a pump 19 via the pipe/well 6.

The present invention, as it is shown and described in the presentapplication, offers several advantages:

1. The pipe separator tolerates high internal and external pressure andtherefore allows the following processing tasks to take place at largesea depths:

-   -   Bulk gas/oil/water or oil/water separation.    -   Removal of water from crude oil to product specifications.        -   A pipe separator in combination with a Compact Electrostatic            Coalescer (Kvaerner technology).        -   A pipe separator in combination with a Pect C Coalescer            (Cyclotech technology).    -   Gas dehydration by means of a combination of gas dehydration        technology (Minox technology) and a pipe separator.

2. It produces a quality of aqueous phase that allows reinjection.

3. Low water content in the oil and gas flows, thus allowingchemical-free hydrate control in connection with transport to downstreaminstallations.

4. The pipe separator tolerates a high internal process pressure and cantherefore be installed to advantage upstream of a choke valve on thewell head. The high process pressure will improve the phase separationproperties and allow reduced use of de-emulsifier or chemical-freeseparation, depending on the fluid properties.

5. For fields with acid oil and the potential for calcium naphthenateprecipitation, sea bed processing with removal of water to 0.5%,performed at a high system pressure (i.e. lower pH in the aqueous phaseon account of more CO in the aqueous phase), will eliminate problematicprecipitation of calcium naphthenate or expensive topside installationsdesigned to handle calcium naphthenate precipitation.

1. An installation arranged on the sea bed for the separation of fluids, comprising at least one separator (1) that is connected to one or more wells, each via an associated well head (2) or similar, and a pipeline, in which the components separated, oil, gas, water or combinations of these substances, are fed fully or partially from the installation to a platform, vessel, etc. on the surface or via collecting pipelines onto shore, or are reinjected into the formation beneath the sea bed, wherein each separator (1) consists of a long pipe (pipe separator) that may form a major or minor part of the transport pipeline (18) from the well and has a diameter that is mainly equal to or slightly larger than the diameter of the transport pipeline (18).
 2. An installation in accordance with claim 1, wherein a first separator (1), which is designed to separate gas and liquid, where the gas separated is fed via a pipeline (3) to the surface/shore, while the liquid separated is fed to a second pipe separator (8) for oil and water, after which the oil separated is fed to the surface/shore via a pump (5) and pipeline (4), while the water separated is reinjected into the reservoir by means of a pump (7) via a pipeline (6).
 3. An installation in accordance with claim 1, wherein a compact electrostatic coalescer (9) is arranged between the first and second pipe separators (1 and 3).
 4. An installation in accordance with claim 1, wherein a gas dehydration unit (11) and a subsequent gas/liquid separator (12) are arranged at the gas outlet from the first separator (11), whereby glycol is added via a pipeline (13) to the dehydration unit (11), while gas separated is fed from the separator (12) to the surface via a pipeline (14) and glycol separated is fed to the surface by means of a pump (16) via a pipeline (15).
 5. An installation in accordance with claim 2, wherein a compact electrostatic coalescer (9) is arranged between the first and second pipe separators (1 and 3).
 6. An installation in accordance with claim 2, wherein a gas dehydration unit (11) and a subsequent gas/liquid separator (12) are arranged at the gas outlet from the first separator (11), whereby glycol is added via a pipeline (13) to the dehydration unit (11), while gas separated is fed from the separator (12) to the surface via a pipeline (14) and glycol separated is fed to the surface by means of a pump (16) via a pipeline (15).
 7. An installation in accordance with claim 3, wherein a gas dehydration unit (11) and a subsequent gas/liquid separator (12) are arranged at the gas outlet from the first separator (11), whereby glycol is added via a pipeline (13) to the dehydration unit (11), while gas separated is fed from the separator (12) to the surface via a pipeline (14) and glycol separated is fed to the surface by means of a pump (16) via a pipeline (15). 